279 research outputs found
A relativistic framework to determine the nuclear transparency from A(p,2p) reactions
A relativistic framework for computing the nuclear transparency extracted
from A(p,2p) scattering processes is presented. The model accounts for the
initial- and final-state interactions (IFSI) within the relativistic
multiple-scattering Glauber approximation (RMSGA). For the description of color
transparency, two existing models are used. The nuclear filtering mechanism is
implemented as a possible explanation for the oscillatory energy dependence of
the transparency. Results are presented for the target nuclei 7Li, 12C, 27Al,
and 63Cu. An approximated, computationally less intensive version of the RMSGA
framework is found to be sufficiently accurate for the calculation of the
nuclear transparency. After including the nuclear filtering and color
transparency mechanisms, our calculations are in acceptable agreement with the
data.Comment: 17 pages, 4 figures, accepted for publication in Phys. Lett.
A relativistic Glauber approach to polarization transfer in 4He(\vec{e},e'\vec{p})
Polarization-transfer components for 4He(\vec{e},e'\vec{p})3H are computed
within the relativistic multiple-scattering Glauber approximation (RMSGA). The
RMSGA framework adopts relativistic single-particle wave functions and
electron-nucleon couplings. The predictions with free and various
parametrizations for the medium-modified electromagnetic form factors are
compared to the world data.Comment: 2 pages, 1 figure Proceedings of the Int. School on Nuclear Physics,
26th Course, Erice (Sicily), September 16th- 24th, 2004; To appear in
Progress in Particle and Nuclear Physic
Model discrimination in pseudoscalar-meson photoproduction
To learn about a physical system of interest, experimental results must be able to discriminate among models. We introduce a geometrical measure to quantify the distance between models for pseudoscalar-meson photoproduction in amplitude space. Experimental observables, with finite precision, map to probability distributions in amplitude space, and the characteristic width scale of such distributions needs to be smaller than the distance between models if the observable data are going to be useful. We therefore also introduce a method for evaluating probability distributions in amplitude space that arise as a result of one or more measurements, and show how one can use this to determine what further measurements are going to be necessary to be able to discriminate among models
Quasi-free (p,2p) and (p,pn) reactions with unstable nuclei
We study (p,2p) and (p,pn) reactions at proton energies in the range of 100
MeV -- 1 GeV. Our purpose is to explore the most sensitive observables in
unpolarized reactions with inverse kinematics involving radioactive nuclei. We
formulate a model based on the eikonal theory to describe total cross sections
and momentum distributions of the recoiled residual nucleus. The model is
similar to the one adopted for knockout reactions with heavy ions. We show that
momentum distributions are sensitive to the angular momentum of the ejected
nucleon which can be used as an spectroscopic tool. The total cross sections
are sensitive to the nucleon separation energies and to multiple scattering
effects. Our calculations also indicate that a beam energy around 500
MeV/nucleon has a smaller dependence on the anisotropy of the nucleon-nucleon
elastic scattering.Comment: 17 pages, 12 figures, Accepted for publication in the Physical review
The exclusive (e,ep) reaction at high missing momenta
The reduced (e,ep) cross section is calculated for kinematics that probe
high missing momenta. The final-state interaction is handled within a
non-relativistic many-body framework. One- and two-body nuclear currents are
included. Electron distortion effects are treated in an exact distorted wave
calculation. It is shown that at high missing momenta the calculated (e,ep)
cross sections exhibit a pronounced sensitivity to ground-state correlations of
the RPA type and two-body currents. The role of these mechanisms is found to be
relatively small at low missing momenta.Comment: 15 pages in REVtex with embedded psfigure
Extracting the Weinberg angle at intermediate energies
A recent experiment by the NuTeV collaboration resulted in a surprisingly
high value for the weak mixing angle . The Paschos-Wolfenstein
relation, relating neutrino cross sections to the Weinberg angle, is of pivotal
importance in the NuTeV analysis. In this work, we investigate the sensitivity
of the Paschos-Wolfenstein relation to nuclear structure aspects at neutrino
energies in the few GeV range. Neutrino-nucleus cross sections are calculated
for O and Fe target nuclei within a relativistic quasi-elastic
nucleon-knockout model.Comment: To appear in the proceedings of International School of Nuclear
Physics: 27th Course: "Neutrinos in Cosmology, in Astro, Particle and Nuclear
Physics", Erice, Sicily, Italy, 16-24 Sep 200
Identifying neutrinos and antineutrinos in neutral-current scattering reactions
We study neutrino-induced nucleon knockout from nuclei. Expressions for the
induced polarization are derived within the framework of the
independent-nucleon model and the non-relativistic plane-wave approximation.
Large dissimilarities in the nucleon polarization asymmetries are observed
between neutrino- and antineutrino-induced processes. These asymmetries
represent a potential way to distinguish between neutrinos and antineutrinos in
neutral-current neutrino-scattering on nuclei. We discuss astrophysical
applications of these polarization asymmetries. Our findings are illustrated
for neutrino scattering on O and Pb.Comment: 5 pages, 5 figures, accepted for publication in Phys. Rev. Let
Electroweak interactions in a relativistic Fermi gas
We present a relativistic model for computing the neutrino mean free path in
neutron matter. Thereby, neutron matter is described as a non-interacting Fermi
gas in beta-equilibrium. We present results for the neutrino mean free path for
temperatures from 0 up to 50 MeV and a broad range of neutrino energies. We
show that relativistic effects cause a considerable enhancement of
neutrino-scattering cross-sections in neutron matter. The influence of the
-dependence in the electroweak form factors and the inclusion of a weak
magnetic term in the hadron current is discussed. The weak-magnetic term in the
hadron current is at the origin of some selective spin dependence for the
nucleons which are subject to neutrino interactions.Comment: 11 pages, 7 figures, accepted to Phys. Rev. C, minor changes and
updates of the figures are mad
Relativistic eikonal approximation in high-energy A(e,e'p) reactions
A fully relativistic model for the description of exclusive (e,e'p) reactions
off nuclear targets at high energies and momentum transfers is outlined. It is
based on the eikonal approximation for the ejectile scattering wave function
and a relativistic mean-field approximation to the Walecka model. Results for
^{12}C(e,e'p) and ^{16}O(e,e'p) differential cross sections and separated
structure functions are presented for four-momenta in the range 0.8 \leq Q^{2}
\leq 20 (GeV/c)^{2}. The regions of applicability of the eikonal approximation
are studied and observed to be confined to proton knockout in a relatively
small cone about the momentum transfer. A simple criterium defining the
boundaries of this cone is determined. The Q^2 dependence of the effect of
off-shell ambiguities on the different (e,e'p) structure functions is
addressed. At sufficiently high values of Q^2 their impact on the cross
sections is illustrated to become practically negligible. It is pointed out
that for the whole range of Q^2 values studied here, the bulk of the
relativistic effects arising from the coupling between the lower components in
the wave functions, is manifesting itself in the longitudinal-transverse
interference term.Comment: 13 pages,11 figure
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